Stock material or miscellaneous articles – Circular sheet or circular blank
Patent
1997-05-27
1999-03-16
Evans, Elizabeth
Stock material or miscellaneous articles
Circular sheet or circular blank
428 644, 428 645, 428 647, 428457, 428913, 43027013, 4304951, 430945, 369283, 369288, B32B 300
Patent
active
058827587
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an optical recording medium, wherein recording, erasing and reading of information by irradiating light is possible, and the recording and erasing of signals are conducted by phase changing.
More specifically, the present invention relates to a phase-change type optical recording medium, wherein recording, erasing and reading of information by irradiating light is possible, and the medium has a structure in which the first protective layer, a recording layer, the second protective layer, and a reflective layer are consecutively deposited in this order on a transparent substrate, the thickness of the first protective layer is in a specified range, further the second protective layer has an absorption coefficient k in a specified range.
According to the optical recording medium of the present invention, unevenness of shapes and sizes of the recording pits can be reduced, whether the state of the recording layer is crystalline or amorphous. As a result, the present invention can provide an optical recording medium having an improvement in erasability and reduction of jitter, and having an excellent error rate.
BACKGROUND OF THE ART
Recently, optical recording media have been paid attention as a material playing a centric role among recording media in a highly information-oriented society, and research thereof has been positively promoted.
Especially, optical-disk among optical recording media are paid attention as the most effective recording medium with the spread of multi-media for the future.
The optical-disk as mentioned above include three types, i.e., the read-only type as represented by a compact disk and a laser disk, the write-once type in which writing of information by a user is possible, and the rewritable type in which rewriting of information is possible. Among them, the rewritable type includes a magnetic optical system and a phase-change system, and in the phase-change system, the material in which the phase change between a crystalline state and an amorphous state is caused, is employed as the recording layer.
In the phase-change system, overwriting is easily possible by irradiating to the recording layer a laser beam the intensity of which is modulated according to recording signals as shown in FIG. 2. That is to say, at the spot where a laser beam having strong power is irradiated for a short time, a material of the recording layer is rapidly heated and melted, and then rapidly cooled, and thereby an amorphous state (a recording pit) is formed, on the other hand, at the spot where a laser beam having power weaker than that is irradiated, the material is raised in temperature to a temperature range which is lower than the melting point thereof and wherein crystallization thereof is possible, and thereby a crystalline state thereof is formed.
Conventionally, in phase-change type optical disk, the amplitude of signals is made to be large, or the functions on the repeated use thereof are aimed to improved; therefore a structure having four layers on a transparent substrate as shown in Fig.1 is mainly used. That is the structure of four layers, wherein on the transparent substrate 1 such as a polycarbonate resin, the transparent first protective layer 2, a recording layer 3, the second protective layer 4, and a reflective layer 5 are consecutively provided, and a transparent material similar to that of the first protective layer is usually used for the second protective layer.
As the protective layer, a mixture of chalcogen compound and oxides, a mixture of nitrides, or the like such as ZnS-SiO.sub.2 is popular and widely used, since they have an excellent protective property on the recording layer, and a mechanical property adequately durable to the repeating of recording and erasing.
Heretofore, for the purpose of improving the recording sensitivity of a phase-change type optical recording medium, a structure has been proposed wherein a protective layer absorptive of light, such as a layer in which metal is dispersed in a dielectric, is prov
Furuya Kazuyuki
Okamura Tatsuya
Suzuki Masaru
Terada Masato
Asahi Kasei Kogyo Kabushiki
Evans Elizabeth
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